The present invention relates to an airship, and more particularly to a stratospheric airship having a gas envelope which is divided by a diaphragm into a buoyant gas compartment containing a buoyant gas therein and an air compartment containing air therein.
Airships are typically used at low altitudes (on the order of kilometer or less) where there is a relatively small change in atmospheric pressure for the purposes of advertisement, relay broadcasting of events, monitoring, security guarding, transportation, sightseeing, etc. For airships used at such low altitudes, the flight altitude control is relatively easy because the flight altitude does not have to be changed over a wide range. Specifically, for such an airship, the volume of the gas envelope is determined so that it can withstand flight at the maximum altitude. After takeoff, the airship is allowed to ascend by throwing ballasts away. After the airship reaches the maximum altitude, the buoyant gas is partially exchanged to the air so as to allow the airship to descend.
In order for an airship to ascend to a high altitude, called the xe2x80x9cstratospherexe2x80x9d (e.g., 17 to 22 Km in altitude), where the atmosphere density is diluted to about {fraction (1/14)} to {fraction (1/15)} of that in the vicinity of the sea level, it is indispensable to provide the airship with a mechanism capable of substantially varying the volume of the buoyant gas for producing a buoyancy such as a helium gas by 14 to 15 folds.
A type of a volume varying mechanism is disclosed in, for example, Japanese Patent Laid-Open Publication No. Sho 54-70597. According to the disclosure, an airship is allowed to descend by winding up the hull of the gas envelope (where the buoyant gas is contained) by means of a roller or by retracting the hull of the gas envelope while squeezing the gas envelope by means of a plurality of rollers opposing one another, so as to reduce the volume of the gas envelope and increase the internal pressure thereof, thereby reducing the static buoyancy. The airship is allowed to ascend by drawing out the hull so as to increase the volume of the gas envelope and reduce the internal pressure, thereby increasing the static buoyancy.
With such a mechanism, however, since the volume of the gas envelope is varied to control the altitude of the airship, the outer shape of the airship changes substantially. This also substantially changes the aerodynamic characteristics of the airship, thereby preventing the airship from ascending with a stable attitude.
FIG. 9 is a schematic side view illustrating another airship in the prior art which addresses this problem. FIG. 10, FIG. 11 and FIG. 12 are cross-sectional views illustrating the same taken along line Vxe2x80x94V, line VIxe2x80x94VI and line VIIxe2x80x94VII in FIG. 9, respectively. Referring to FIG. 10, the airship has a gas envelope 101 defined by a balloon-shaped ship hull 102, and the gas envelope 101 is divided by a diaphragm 103, which acts as a diaphragm, into a buoyant gas compartment 104 containing a buoyant gas therein and an air compartment 105 containing air therein.
Referring to FIG. 11, a thin film buoyant gas tank 106 is provided in an upper portion of the buoyant gas compartment 104. Referring to FIG. 9, ballonets 107 are provided in a front and a rear portion of the air compartment 105 for maintaining the shape of the ship hull 102, i.e., the shape of the gas envelope 101, and for keeping the balance of the airship. Moreover, a solar battery module 108 is provided on the upper surface of the gas envelope 101, and a load 109 including equipment, a storage battery, a fuel cell, mission payload equipment, etc., is suspended from the bottom of the gas envelope 101. The solar battery module 108 and the storage battery, etc., are connected to each other via power cables 110 provided therebetween along the outer surface of the gas envelope 101.
Referring to FIG. 11 and FIG. 12, while the airship is still on the ground before takeoff, a buoyant gas, e.g., a helium gas, is introduced via a buoyant gas inlet 111 into the thin film buoyant gas tank 106, and the valve of the buoyant gas inlet ill is closed. Then, the ambient air is introduced via an air blower 112 into the air compartment 105 so as to pressurize the air compartment 105 to maintain the shape of the ship hull 102. At this time, an air vent valve 113 of the air compartment 105 is closed, and the diaphragm 103 is pushed up, whereby the thin film buoyant gas tank 106 and the buoyant gas supplied from the thin film buoyant gas tank 106 into the buoyant gas compartment 104 are pressurized, as illustrated in FIG. 12.
The airship starts ascending by an excessive buoyancy which is equal to the buoyancy provided by the buoyant gas in the buoyant gas compartment 104 and the thin film buoyant gas tank 106 minus the total weight of the airship including the equipment. As the airship ascends, the atmospheric pressure gradually decreases. Along with the decrease in the atmospheric pressure, the difference between the internal pressure of the gas envelope 101 and the atmospheric pressure gradually increases. In order to keep the pressure difference within a predetermined limit, the air vent valve 113 is opened so as to discharge the air from the air compartment 105 and to reduce and adjust the volume of air therein. The adjustment of the volume of air causes a difference between the pressure in the thin film buoyant gas tank 106 and that in the buoyant gas compartment 104. In order to keep the pressure difference at or below a predetermined pressure, a buoyant gas bent valve 114 is opened so as to transfer the buoyant gas from the thin film buoyant gas tank 106 into the buoyant gas compartment 104.
The buoyant gas transferred into the buoyant gas compartment 104 expands, thereby ensuring a sufficient excessive buoyancy for the airship to continue to ascend, and compensates for the reduction in the volume of air due to the discharge of air, thereby constantly maintaining the volume within the ship hull 102 and thus substantially constantly maintaining the outer shape of the gas envelope 101.
After the airship has ascended into the stratosphere, the airship keeps a station in the air, with the gas envelope 101 being in a state as illustrated in FIG. 13. The volume of air in the air compartment 105 has been substantially reduced, and the diaphragm 103 has been pushed down by the expanded buoyant gas in the buoyant gas compartment 104 while the airship keeps a station in the stratosphere.
With the conventional airship as described above, the difference between the internal pressure of the gas envelope 101 and the atmospheric pressure which is caused by the atmospheric pressure decreasing along with the ascent of the airship is accommodated by reducing and adjusting the volume of air in the air compartment 105 so as to allow the buoyant gas to expand, thereby ensuring a sufficient excessive buoyancy. Moreover, the reduced volume of air is compensated for by the increased volume of the buoyant gas, thereby constantly maintaining the volume of the gas envelope 101. Thus, the outer shape of the gas envelope 101, i.e., the outer shape of the airship is substantially constantly maintained.
However, the diaphragm 103 for partitioning the buoyant gas compartment 104 and the air compartment 105 from each other is a very large sheet of film which is coupled along its periphery to the ship hull 102. Therefore, it is difficult for the diaphragm 103 to smoothly change its shape to closely follow the increase in the volume of the buoyant gas occurring along with the decrease in the volume of air in the air compartment 105. For example, as illustrated in FIG. 14, the diaphragm 103 may experience xe2x80x9csloshingxe2x80x9d (i.e., a phenomenon in which the diaphragm 103 takes a wavy shape), thereby causing an asymmetric distribution of the buoyant gas in the gas envelope 101. The asymmetric distribution of the buoyant gas may disturb the balance of the buoyancy, thereby preventing the airship from stably ascending into the stratosphere. As a result, the size of the diaphragm 103 is limited, thereby also limiting the range over which the ratio between the volume of the buoyant gas and the volume of air can be varied.
Moreover, since the load 109 is suspended from the bottom of the gas envelope 101, a load weight W directly acts upon lower side faces of the ship hull 102. As a result, as illustrated in FIG. 15, the gas envelope 101 is deformed from the cross-sectional shape as illustrated in a one-dot chain line to a generally elliptical cross-sectional shape, thus deforming the outer shape of the gas envelope 101, thereby causing an asymmetric distribution of the buoyant gas in the buoyant gas compartment 104. The asymmetric distribution of the buoyant gas disturbs the balance of the buoyancy, which may reduce the aerodynamic stability, thereby preventing the airship from stably ascending. Moreover, the suspension of the load 109 requires a reinforcing member such as a reinforcing doubler for ensuring a sufficient strength in the lower side faces of the ship hull 102 upon which the load weight W acts, thereby causing an increase in the total weight of the airship.
Furthermore, the power cables 110 connecting the solar battery module 108 and the storage battery to each other are provided exposed along the outer surface of the gas envelope 101. Therefore, the power cable is long, thereby increasing the possible power loss therealong and the total weight of the airship. Moreover, since the power cables 110 are exposed, they may create an adverse aerodynamic drag.
Thus, the present invention has been made in view of these problems in the prior art, and an object of the present invention is to provide a stratospheric airship capable of substantially and smoothly varying the volume of a buoyant gas so as to allow the airship to stably ascend into the stratosphere and keep a station therein.
In order to achieve the object of the present invention as described above, according to a first aspect of the invention there is provided a stratospheric airship, comprising a gas envelope defined by a ship hull, a flexible diaphragm for vertically dividing the gas envelope into a buoyant gas compartment containing a buoyant gas and an air compartment containing air, the diaphragm being coupled along a periphery of the diaphragm to the ship hull generally at a midpoint along a vertical dimension of the ship hull, and a diaphragm supporting member for coupling a central portion of the diaphragm to a central portion of the gas envelope generally at a midpoint along a vertical dimension of the gas envelope, wherein the stratospheric airship can be ascended by varying a volume ratio between the buoyant gas contained in the buoyant gas compartment and the air contained in the air compartment.
In the first aspect of the present invention, even if the shape of the diaphragm changes along with the change in the volume ratio between the air contained in the air compartment and the buoyant gas contained in the buoyant gas compartment, a central portion of the diaphragm is coupled to a diaphragm supporting member in a central portion of the gas envelope generally at the midpoint along the vertical dimension of the gas envelope, whereby the central portion of the diaphragm is substantially fixed to a predetermined position, thereby suppressing the sloshing phenomenon. Thus, even if the change in the shape of the diaphragm occurred, such a change would be symmetric or generally symmetric about the central portion of the diaphragm in a well-balanced manner. As a result, an asymmetric distribution of the buoyant gas in the buoyant gas compartment never occurs, thereby ensuring a good balance of the buoyancy from the buoyant gas. Therefore, it is possible to substantially and smoothly vary the ratio between the volume of the buoyant gas in the buoyant gas compartment and the volume of air in the air compartment so as to allow the airship to stably ascend into the stratosphere and keep a station therein.
According to a second aspect of the present invention, in the stratospheric airship according to the first aspect, the diaphragm supporting member is a suspension chord extending along a vertical direction in the gas envelope, with an upper end of the suspension chord being coupled to a central portion of an upper surface of the ship hull and with a lower end of the suspension chord being coupled to a central portion of a lower surface of the ship hull, and further the central portion of the diaphragm is coupled to the suspension chord generally at a midpoint along a vertical dimension of the suspension chord.
In the second aspect of the present invention, the diaphragm supporting member for supporting the central portion of the diaphragm can be easily provided as a suspension chord which extends in the vertical direction in the gas envelope and whose upper and lower ends are coupled to the central portions of the upper and lower surfaces of the ship hull, respectively.
According to a third aspect of the present invention, in the stratospheric airship according to the second aspect, the suspension chord passes through a center line, the center line running in a horizontal direction of the gas envelope.
In the third aspect of the present invention, the suspension chord is provided to pass through the center line of the gas envelope, thereby suppressing the sloshing phenomenon. Thus, the change in the shape of the diaphragm, even if it occurred, would be left-right symmetric or generally left-right symmetric about the central portion in a well-balanced manner, thereby more reliably ensuring a good balance of the buoyancy from the buoyant gas. Thus, it is possible to vary more smoothly the volume ratio between the buoyant gas and the air, thereby ensuring a stable ascent operation.
According to a fourth aspect of the present invention, in the stratospheric airship according to the third aspect, a plurality of the suspension chords are provided to be parallel to one another and perpendicular to the center line.
In the fourth aspect of the present invention, even if the shape of the diaphragm changes along with the change in the volume ratio between the air contained in the air compartment and the buoyant gas contained in the buoyant gas compartment, a central portion of the diaphragm is coupled to a series of suspension chords which are provided to be parallel to one another and perpendicular to the center line, whereby the central portion of the diaphragm is fixed at a plurality of positions along the center line, thereby more effectively suppressing the sloshing phenomenon. Thus, even if the change in the shape of the diaphragm occurred, such a change would be left-right symmetric or generally left-right symmetric about the central portion of the diaphragm. As a result, the left-right balance of the buoyancy from the buoyant gas is more reliably ensured. Therefore, even with a relatively large gas envelope, it is possible to smoothly vary the volume ratio between the buoyant gas in the buoyant gas compartment and the air in the air compartment, thereby achieving a stable ascent operation.
According to a fifth aspect of the present invention, in the stratospheric airship according to the second aspect, a load supporting member provided under a bottom surface of the ship hull is suspended from the lower end of the suspension chord.
In the fifth aspect of the present invention, the load supporting member carrying the load is suspended from the lower end of the suspension chord which is coupled at its upper end to a central portion of the upper surface of the ship hull, passes through the gas envelope, and is coupled at its lower end to a central portion of the bottom surface of the ship hull. Thus, the load weight of the load supporting member and the load directly acts upon the central portion of the upper surface of the ship hull via the suspension chord. As a result, the load weight of the load supporting member and the load acts downwardly via the suspension chord upon a central portion of the upper surface of the buoyant gas compartment upon which the buoyancy from the buoyant gas acts, thereby suppressing the deformation of the upper surface of the ship hull due to the buoyancy. Thus, the shape of the buoyant gas compartment is maintained, thereby suppressing the asymmetric distribution of the buoyant gas therein, and thus ensuring a good balance of the buoyancy. Moreover, the shape of the gas envelope is maintained, thereby providing an aerodynamic stability to the airship.
According to a sixth aspect of the present invention, in the stratospheric airship according to the fifth aspect, the load supporting member and a load carried by the load supporting member are enclosed in a thin film fairing, which is coupled along a periphery of the thin film fairing to the bottom surface of the ship hull, and further provides a function of layering airstream, and a tension of the thin film fairing restricts a sloshing of the load supporting member and the load.
In the sixth aspect of the present invention, the sloshing of the load supporting member and the load is restricted by the tension of the thin film fairing which also provides a function of layering the stream, the suspended load supporting member, the load, etc., are held in a stable manner, and it is possible to eliminate separate means for restricting the sloshing, thereby simplifying the structure and reducing the total weight of the structure.
According to a seventh aspect of the present invention, in the stratospheric airship according to the second aspect, a power cable is provided coaxially with or in parallel to the suspension chord.
In the seventh aspect of the present invention, the power cable is provided to pass through the gas envelope, thereby shortening the power cable and reducing the possible power loss therealong and the total weight of the airship as compared to the case of the conventional airship where the power cable is provided along the outer surface of the ship hull. Moreover, the power cable is not exposed on the outside, thereby reducing the air drag.
According to an eighth aspect of the present invention, in the stratospheric airship according to the seventh aspect, the power cable connects a solar battery module provided on the upper surface of the ship hull to a load provided under the lower surface of the ship hull.
In the eighth aspect of the present invention, the power cable for connecting the solar battery module to the load carried by the load supporting member, e.g., a storage battery, is provided coaxially with or in parallel to the suspension chord which passes through the gas envelope and connects a central portion of the upper surface of the ship hull 11 to a central portion of the lower surface of the ship hull 11. Thus, the power cable is provided via the shortest route, thereby shortening the power cables and reducing the possible power loss therealong and the total weight of the airship as compared to the case of the conventional airship where the power cable is provided along the outer surface of the gas envelope. Moreover, the power cable is not exposed on the outside, thereby reducing the air drag.